A 25-year-old develops urticaria, angioedema, and bronchospasm within minutes of a penicillin injection. This reaction is mediated by:

• A IgG and complement (Type II hypersensitivity)
• B Immune complexes depositing in vessel walls (Type III hypersensitivity)
• C IgE bound to mast cells and basophils (Type I hypersensitivity) ✓
• D CD8+ cytotoxic T lymphocytes (Type IV hypersensitivity)

Explanation

Anaphylaxis and atopic reactions are Type I (immediate) hypersensitivity, mediated by allergen cross-linking IgE molecules bound to high-affinity FcεRI receptors on mast cells and basophils, triggering degranulation of preformed mediators (histamine, tryptase, heparin) and synthesis of lipid mediators (leukotrienes, prostaglandins). Urticaria, angioedema, and bronchospasm ensue within minutes. Type II hypersensitivity involves cytotoxic antibodies; Type III involves immune complexes; Type IV is delayed-type (T cell-mediated, 48–72 h).

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.